The fuselage of a modern aircraft typically includes multiple fuselage barrels that have an outer skin, which is supported by circular frame structures. The frame structures reside within the skin and are positioned in a parallel configuration and at given intervals. The frame structures are attached to the skin via shear ties, which are fastened to the skin. Longerons are integrally formed with the skin and extend between the shear ties to provide increased rigidity and strength. Doublers are also formed with the skin to provide increased strength in doorway and window areas.
A one-piece or 360° integrally formed fuselage barrel can, for example, be in the form of a sandwich structure or in the form of a monolithic structure. The tooling commonly used to form a one-piece fuselage barrel that has a skin, longerons, and doublers, uses a series of large mandrel segments, which are joined to each other in a radial orientation. For example, the tooling for an aircraft fuselage barrel that is approximately 40 feet long may have six mandrel segments that are each 40 ft long and are coupled in series circumferentially. The skin, longerons, and doublers are “laid-up” onto the segments and cured to form the fuselage. After curing, the mandrels are decoupled and removed from the fuselage barrel. The segments are heavy, and difficult to handle and extract from the fuselage barrel. Each fuselage barrel in the aircraft industry typically has its own set of mandrel segments.
Other approaches have been utilized to form a one-piece fuselage barrel. One of these approaches utilizes mandrel segments that are relatively smaller in diameter as compared to the method described above. The mandrel segments are wrapped with an inflatable bag. A sandwiched fuselage barrel structure, including the inner and outer skins, the core, and the doublers, is laid-up onto the bag. Stable cowlings are placed over the sandwiched structure and the bag is inflated to apply an outward pressure on the sandwiched structure and to press the skin against the cowlings. Upon curing of the fuselage barrel the bag is deflated and the mandrel segments are removed. Although this approach somewhat eases the manipulation of the mandrel segments due to reduced diameter and weight of the mandrels, it is generally better suited for sandwich structures and cannot be easily applied to complex monolithic structures.
Another approach utilizes long continuous mandrel segments. Skins, longerons, and doublers are laid-up onto the mandrel segments and cowling plates are applied and pressed thereon. A bag is extended over the exterior of the cowling plates. The bag applies pressure to the cowling plates via a generated vacuum therein. Although this approach allows for the integral formation of the skin, longerons, and doublers, it does not allow for the integration of shear ties and/or frames. In addition, due to the size and weight, this approach also uses mandrel segments that are difficult to handle and extract.
Thus, there exists a need for an improved, simplified, and efficient technique of forming a one-piece aircraft fuselage barrel.